Tim McGraw turned to social media to share his best wishes and prayers for Senator John McCain (R - Ariz.) on Thursday (July 20), calling the veteran legislator a "real good man."

McCain made headlines when he underwent surgery to remove a blood clot last Friday (July 14), but the seemingly routine procedure turned very serious on Wednesday (July 19), when the Mayo Clinic Hospital in Phoenix announced that tests had revealed a cancerous brain tumor in the 80-year-old senator.

McGraw shared an old black-and-white photo of the U.S. Navy veteran and war hero in his old uniform to Instagram on Thursday, captioning the photo, "real good man and A REAL HERO...... Prayers from the McGraw family, @senjohnmccain."

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CNN reported Wednesday that McCain has been diagnosed with a primary glioblastoma, which is a very aggressive tumor that forms in the tissue of the brain and spinal cord, according to the American Brain Tumor Association. A post-surgery scan shows the cancerous tissue has all been removed, and McCain is resting at his home in Arizona. He and his family are considering treatment options, which his doctors say are likely to include radiation and chemotherapy.

A statement from McCain's office says he is doing "amazingly well," but it is currently unknown when he will be able to return to work. It won't be long if McCain has much to say about it; on Thursday the ultra-tough senator tweeted, "I greatly appreciate the outpouring of support - unfortunately for my sparring partners in Congress, I'll be back soon, so stand-by!"